In an opinion released Wednesday, U.S. District Judge John Keenan ruled that the plaintiffs could introduce testimony by two doctors to show that the drug can cause jaw damage after less than three years of continuous use.

Keenan said the evidence is sufficiently reliable to allow a rational jury to establish such a connection. He said individual plaintiffs will then be allowed to present expert testimony that Fosamax caused them to suffer such damage, and that such testimony could by itself "make causation a genuine issue of fact for trial."

Merck was not immediately available for comment.

The company faces a slew of lawsuits involving almost 900 cases by patients who say Fosamax caused osteonecrosis of the jaw. A Manhattan jury is deliberating this week over the drug company's potential liability in one such case.